Embodiments of the present invention relate to a method of testing for a leakage current between bit lines of a nonvolatile memory device and, more particularly, to a method of testing for a leakage current between the bit lines of a nonvolatile memory device, the method having an improved accuracy.
The memory cell array of a NAND flash memory device of nonvolatile memory devices includes a number of strings in each of which a number of memory cells are coupled in series to one bit line. In the flash memory device constructed as above, the spacing between the bit lines is made relatively narrow in order to reduce the chip size. This brings neighboring bit lines in contact with each other because of processing failures. Consequently, a leakage current can occur between bit lines because of a bridge phenomenon.
FIG. 1 is a circuit diagram of a conventional nonvolatile memory device. A conventional method of testing for a leakage current between bit lines is described below with reference to FIG. 1.
First, a discharge signal DISCHe is supplied to a bit line selection unit 10, and so a test voltage VIRPWR of about 1 V is supplied to the even bit line BLe of a memory cell array. A discharge signal DISCHo of a low level is supplied and the even bit line BLo of the memory cell array is maintained in a floating state.
When the discharge signal DISCHe shifts to a low level, a bridge may occur between the even bit line BLe and the odd bit line BLo. Accordingly, the voltage level of the even bit line BLe drops from a precharged voltage level if the bridge occurs or maintains an initial precharge level if the bridge fails to occur.
A page buffer 20 detects a shift in the voltage level of the even bit line BLe and outputs a pass or fail signal of the test operation based on a result of the detection.
In the conventional method of testing for a leakage current between the bit lines of the nonvolatile memory device, an evaluation time period is desired not to be long because the leakage current and an off-cell leakage current are generated through a junction. Further, it is difficult to detect the leakage current between the bit lines because a difference in the voltage level between the even bit line BLe and the odd bit line BLo is small and therefore, the leakage current is small.